Multistage drawing process for polybenzimidazole strand material

ABSTRACT

Foamable polybenzimidazole fiber or yarn is hot drawn without foaming at a draw ratio above about 1.5:1 and at a drawing speed in excess of about 20 meters per minute in a drawing zone wherein the fiber is radiantly heated and wherein the draw is effected on at least two passes through the zone, the drawn on any one pass being less than about 1.5:1.

O Umted States Patent 11113,622,660

[72] Inventors George F. Ecker [56] References Cited 1857 Shiff Court, Toms River, NJ. 08753; UNITED STATES PATENTS a? ,gZ, 2,624,934 1/1953 Munson et al. 264/290 A l N 1 3,081,485 3/1963 Steigerwald 264/26 [21] i 0623 1968 3,441,640 4/1969 Santangelo 264/290 lf 1971 3,502,756 3/1970 Bohrer et al. 264/210 Continuation-impart of application Ser. No. Primary Home 520,743, Ja 14, 195 now abandoned Assistant Examiner-Herbert Mintz Thi application 0 23, 1963, s Anomeys-Thomas J Morgan, Charles B. Harris and Burns, 769,862 Doane, Benedict;Swecker & Mathis [54] MULTl-STAGE DRAWING PROCESS FOR ABSTRACT: Foamable polybenzimidazole fiber or yarn is hot POLYBENZIMIDAZOLE STRAND MATERIAL drawn without foaming at a draw ratio above about 1.5:] and 11 Claim 1 Dn i Fi at a drawing speed in excess of about 20 meters per minute in a drawing zone wherein the fiber is radiantly heated and [52] U.S. Cl 264/290 R, wherein the draw is effected on at least two passes through the [51] Int. Cl zone, the drawn on any one pass being less than about 1.521. [50] Field ofSearch 264/210,

MULTISTAGE DRAWING PROCESS FOR POLYBENZIMIDAZOLE STRAND MATERIAL BACKGROUND OF THE INVENTION The present invention relates to a process for improving the tensile properties such as tenacity of foamable polybenzimidazole fibers, filaments, yarns and the like, sometimes hereinafter referred to generally as strand material. More particularly, the present invention relates to a process for hot drawing foamable polybenzimidazole fiber of yarn whereby the foaming or exploding problem is overcome or eliminated thereby yielding a polybenzimidazole fiber having improved tensile properties.

I-Iot drawing or stretching polymer fibers is a well known method for increasing the fiber tensile properties, particularly tenacity. It has been found, however, that when foamable polybenzimidazole fiber, as hereinafter defined, however, that when foamable polybenzimidazole fiber, as hereinafter defined, and particularly foamable aromatic polybenzimidazole fiber is subjected to a hot drawing operation the fiber will foam or explode during the operation resulting in a porous fiber product having relatively low tensile properties.

Heretofore, it was believed that the foaming problem was due in large part to the presence of water in the polybenzimidazole fiber, the water having been pipicked up" primarily during the water washing step used to remove residual spinning solvent from the fiber. However, it has since been found that even when the polybenzimidazole fiber is dried to remove essentially all of the wash liquid such as water, the resulting fiber frequently still foams during the hot drawing operation. Thus, drying alone is not the solution. It appears that certain unknown volatile materials that may be formed during the polybenzimidazole polymerization reaction and which tenaciously adhere or are chemically bound to the fibers may be chiefly responsible for the foaming problem during hot drawing.

Several methods have been suggested for overcoming the foaming problem. For example, the deleterious foaming and exploding can be reduced by hot drawing at low speeds, that is, the speed of the supply roll, on on the order of 5 meters a minute. However, such drawing operations are too slow to permit large scale economic production.

Similarly, the foaming and exploding can be reduced by hot drawing at low draw ratios on the order of about l.5:l or less, for example, as determined by the ratio of the surface speed of the takeup or stretch roll to the surface speed of the supply roll. However, such low draw ratios are undesirable because a high degree of orientation cannot thereby be achieved, and fibers of low orientation have low tenacity values.

It has also been suggested that the foaming problem can be eliminated by subjecting the foamable polybenzimidazole fiber to a heat treatment prior to hot drawing, that is, a nondegrading heat treatment, at a temperature in the range of from about 50 C. below the hot drawing temperature'up to the degradation temperature of the polybenzimidazole fiber for a period of time of at least about one second. Such a scheme of course requires the additional preheating step and the equipment associated therewith.

In short, there is no presently known process for hot drawing foamable polybenzimidazole fiber without foaming at practical drawing speeds and draw ratios. e.g., above about 5 to meters per minute and above about 1.5:1 respectively, which does not necessitate some form of pretreatment such as preheating.

Accordingly, the primary object of the present invention is to provide a process for improving the tensile properties of foamable polybenzimidazole fiber or yarn. Another object is to provide a process for hot drawing foamable polybenzimidazole fiber without foaming. Still another object of the present invention is to provide a process for hot drawing foamable polybenzimidazole fiber without foaming at practical drawing speeds and draw ratios without the necessity for any special pretreatment prior to the hot drawing operation. These and other objects will be apparent from the following description.

In accordance with the present invention, foamable polybenzimidazole fiber or yarn, that is, strand material, is hot drawn without foaming by introducing the fiber into a hot drawing zone wherein the fiber us radiantly heated and drawing the fiber therein at a draw ratio of about l.5:l and at a drawing speed in excess of about 20 meters per minute. The draw is effected or imparted to the fiber or yarn on at least two passes of the fiber through the zone, the draw on any one pass being less than about l.5: l.

The term foamable polybenzimidazole fiber or yarn is meant to include any and all polybenzimidazole fiber or yarn (strand material) which undergoes foaming or exploding or both during hot drawing, that is, drawing at a temperature above about 400 C., particularly when the hot drawing is at a draw ratio of above about 1.5: l and at a drawing speed in excess of about 5 to 10 meters per minute.

It is important to note that not all polybenzimidazole strand material undergoes foaming during hot drawing, irrespective of the drawing speeds and ratios and any pretreatments. However, there is no present method for determining whether or not foaming will occur without actually hot drawing the material in a simple test run. Hence, if foaming does occur, the hot drawing process of the present invention may be employed.

DETAILED DESCRIPTION OF THE INVENTION For a better and more complete understanding of the present invention, its objects and advantages, reference should be had to the following detailed description and to the accompanying drawing which is an illustration of a suitable hot drawing zone or apparatus which may be used in ac cordance with the present invention.

THE STARTING POLYMER Polybenzimidazoles are a known class of heterocyclic polymers which consist essentially of recurring units of the following formulas and II. Formula I is:

wherein R is a tetravalent aromatic nucleus, with the nitrogen atoms forming the benzimidazole rings being paired upon adjacent carbon atoms, i.e., ortho carbon atoms, of the aromatic nucleus, and R is a member of the class consisting of an aliphatic (alkylene) group, a cycloaliphatic ring, an aromatic ring and a heterocyclic ring such as pyridine, pyrazine, furan, quinoline, thiophene, and pyran. Formula II is:

wherein Z is an aromatic nucleus having the nitrogen atoms forming the benzimidazole ring paired upon the adjacent carbon atoms of the aromatic nucleus.

Preferably, the fibers or yarns subjected to the hot drawing process of the present invention are prepared from aromatic polybenzimidazoles, that is, from polymers consisting essentially of the recurring units of formula II and of Formula I wherein R is an aromatic ring or a heterocyclic ring.

As set forth in US. Pat. No. 3,l74,947 and Reissue Pat. No. 26,065, which are incorporated herein by reference, the aromatic polybenzimidazoles having the recurring units of Formula II may be prepared by self-condensing a trifunctional aromatic compound containing only a single set of ortho disposed diamino substituents and an aromatic, preferably phenyl, carboxylate ester substituent. Exemplary of polymers of this type is poly-2,5(6)-benzimidazole prepared by the autocondensation of phenyl-3,4diaminobenzoate.

As also set forth in the above-mentioned patents, the aromatic polybenzimidazoles having the recurring units of Formula I may be prepared by condensing an aromatic tetraamine compound containing a pair of orthodiamino substituents on the aromatic nucleus with a dicarboxyl compound selected from the class consisting of (a) the diphenyl ester of an aromatic dicarboxylic acid, (b) the diphenyl ester of a heterocyclic dicarboxylic acid wherein the carboxyl groups are substituents upon carbon in a ring compound selected form the class consisting of pyridine, pyrazine, furan, quinoline, thiophene and pyran and (c) an anhydride of an aromatic dicarboxylic acid.

Examples of aromatic polybenzimidazoles which have the recurring structure of Formula I and which may be formed into fibers or yarns and subjected to the hot drawing process of the present invention include: poly-2,2'(m-phenylene) 5,5'-bibenzimidazole; poly-2,2'(pyridylene-3", 5")-5,5' -bibenzimidazole; poly-2,2'-(furylene-2 ,5 )-5 ,5 '-bibenzimidazole; poly-2,2-(naphthalene-l 6" )-5 ,5 '-bibenzimidazole; poly-2,2-(biphenylene3"4"')-5,5'-bibenzimidazole; poly-2,2-amylene-5,5'-bibenzimidazole; poly-2,2'-octamcthylene-5,5 '-bibenzimidazole; poly-2,6-( m-phenylene )-diimidazobenzene; poly-2,2'-cyclohexenyl-5,5-bibenzimidazole; poly-2,2'( m-phenylcne )-5,5 '-di( benzimidazolene) ether; poly-2,2'-(m-phenylene )-5,5-di(benzimidazolene) sulfide; poly-2,2( m-phenylene )-5,5 -di( benzimidazolene) sulfone; poly-2,2'-(m-phenylene )-5,5-di( benzimidazolene) methane; poly-2',2"(m-phenylene)-5',5"di(benzimidazolene) propane-2,2; and poly-2'2"(m-phenylene)-5',5"di(benzimidazole)ethylenel,2 where the double bonds of the ethylene groups are intact with the final polymer.

The preferred aromatic polybenzimidazolene fiber or yarn is one prepared from the poly-2,2-m-phenylene)-5,5- bibenzimidazole, the recurring unit of which is:

Any polymerization process known to those skilled in the art may be employed to prepare the polybenzimidazolene which may then be spun into fiber and if it foams during hot drawing, i.e., is foamable polybenzimidazole fiber, subjected to the hot drawing treatment of the present invention.

With respect to aromatic polybenzimidazoles, preferably equimolar quantities of the monomeric tetraamine are dicarboxyl compound are introduced into a first stage melt polymerization reaction zone and heated therein at a temperature above about 200 C., preferably at least 250' C., and more preferably from about 270 C. to 300 C. The reaction is conducted in a substantially oxygen-free atmosphere, i.e., below about p.p.m. oxygen and preferably below about 8 ppm. oxygen, until a foamed prepolymer is formed. Usually, the first stage reaction is continued until a prepolymer is formed having an inherent viscosity, expressed as deciliters per gram, of at least 0.1 and preferably from about 0. l 3 to 0.3, the inherent viscosity (l.V.) as used in the present specification and claims being determined from a solution of 0.4 grams of the polymer in 100 ml. of 97 percent H 80, at C.

After the conclusion of the first stage reaction, which normally takes at least 0.5 hours and preferably 1 to 3 hours, the foamed prepolymer is cooled and then powered or pulverized in any convenient manner. The resulting prepolymer powder is then introduced into a second stage polymerization reaction zone wherein it is heated under substantially oxygen-free conditions, ad described above, to yield a polybenzimidazole polymer product, desirably having an l.V., as measured above,

ofat least 0.6, e.g., 0.80 to [.1 or more.

The temperature employed in the second stage is at least 250 C., preferably at least 325 C., and more preferably from about 350' to 425 C. The second stage reaction generally takes at least 0.5 hours, and preferably from about 1 to 4 hours or more.

Preparation of the Fiber As is well known, the polybenzimidazoles are generally formed into fibers or filaments by solution spinning, that is, by dry or wet spinning a solution of the polymer in an appropriate solvent such as dimethylacetamide, dimethylformamide, dimethylsulfoxide or sulfuric acid (used only in wet spinning) through an opening of predetermined shape into an evaporative atmosphere for the solvent in which most of it is evaporated (dry) or into a coagulation bath (wet), resulting in the polymer having the,desired shape.

The polymer solutions may be prepared, for example, by dissolving sufficient polybenzimidazoles in the solvent to yield a final solution suitable for extrusion containing from about 10 to 45 percent by weight of polymer, based on the total weight of the solution, preferably from about 20 to 30 percent by weight.

One suitable means for dissolving the polymer in the solvent is by mixing the materials at a temperature above the atmospheric boiling point of the solvent, for example, 25 to C. above such boiling point, and at a pressure of 2 to 15 atmospheres for a period of l to 5 hours.

Preferably, the above polymer solutions, after suitable filtration to remove any undissolved portions, are dry spun. For example, the solutions may be extruded through a spinneret into a conventional type downdraft spinning column containing a circulating inert gas such as nitrogen, noble gases, combustion gases or super heated steam. Conveniently, the spinneret face is at a temperature of from about to H0 C., the top of the column from about [20 to 220 C., the middle of the column from about to 250 C., and the bottom of the column from about to 320 C. After leaving the spinning column, the fibers are taken up, for example, at a speed in the range of from about 50 to 350 meters per minute. The resulting as spun fibers are then preferably subjected to a slight steam drawing treatment at a draw ratio of from about l.l:l to 1.5: I. This prewash drawing treatment is to be distinguished from the postwash hot drawing process of the present invention. The prewash drawing is employed in order to prevent the fibers from relaxing and falling off the bobbin during the subsequent washing step.

Desirably, the fibers are next washed so as to remove residual spinning solvent, e.g., so that the washed fiber contains less than about 1 percent by weight solvent. based on the weight of the fiber, and preferably so as to obtain an essentially spinning solvent-free fiber. Typically, a simple water wash is employed, however, if desired other wash materials such as acetone, methanol, methyl ethyl ketone and similar dimethylacetamide-miscible and volatile organic solvents may be used in place of or in combination with the water. The washing operation may be conducted by collecting the polybenzimidazole fiber on perforated rolls or bobbins, immersing the rolls in the liquid wash bath and pressure washing the fiber, for example, for about 2 to 48 hours or more.

The washed fibers are then dried in any suitable type of apparatus such as an electric oven to remove at least the major portion of the wash liquid, for example, at least 60 percent by weight, of the wash liquid, preferably at least 90 percent by weight and more preferably, essentially all of the wash liquid. lf substantially less than about 60 percent of the wash liquid is removed prior to subjecting the fiber to hot drawing, the fiber may undergo foaming therein merely due to the excessive wash liquid content. As previously mentioned, however, even if essentially all of the wash liquid is removed, this alone will not overcome the foaming problem which occurs with foamable polybenzimidazole fiber during hot drawing, clearly indicating that the solution to the foaming problem is merely drying.

The drying operation is conveniently conducted at a temperature of from about 150 to 300 C. for about 2 to 100 hours or more. Preferably, the drying temperature does not exceed about 250 C. as above this temperature degradation of the fiber may occur, particularly if an extended heating period, i.e., several hours, is employed.

Hot Drawing As previously mentioned, the essence of the present invention is the discovery of a process for hot drawing, without foaming, foamable polybenzimidazole strand material, without the need for any special pretreatment step, at practical drawing speeds and drawing ratios.

This is accomplished by hot drawing foamable polybenzimidazole fiber or yarn in a radiantly heated drawing zone or apparatus, that is, a zone wherein essentially all of the heat supplied to the fiber or yarn to effect the hot drawing is radiant heat. In other words, little if any heating of the strand material is due to the material contacting a heated surface, for example, such as when a conventional hot shoe, roll, plate or pin is used.

However, in addition to a radiantly heated drawing zone, it has been found that the drawing of the fiber or yarn must occur on at least two or preferably three or more passes of the material through the zone. In other words, all of the desired draw, i.e., draws in excess of about 1.5:1, cannot be imparted to the strand material on one pass through the zone or foaming will occur. The drawing that takes place on any one pass through the zone must be less than about 1.511, for if it is greater, for example, 1.7:] or higher, foaming will normally occur, particularly at drawing speeds on the order of 50 meters per minute.

A typical radiantly heated drawing apparatus or zone which may be used in the present invention is shown in the drawing.

With reference to the drawing, foamable polybenzimidazole fiber denoted by the numeral 1 is conveyed from any conventional type roll or bobbin 2 and wound around a supply or feed roll 3 and a skewed idler roll 4. Desirably, the fiber makes several helical wraps around the supply roll 3 and skewed roll 4 to insure against slippage during the subsequent drawing operation.

The fiber is conducted over a conventional centering guide 9 and through a cylindrical elongated furnace 5 containing a source of infrared radiant heat such as nichrome wire heaters 6. Any other suitable means for supplying the radiant heat may also be used if so desired.

The fiber passes through the furnace 5, makes a one-half wrap around a groove in the grooved idler roll 7, and is then passed back through the furnace 5. Again, upon emerging from the furnace the fiber makes a one-half wrap around a groove in the grooved idler roll 8 and is again passed back through the furnace. Upon exiting from the furnace on the last pass, the fiber is passed over another centering guide 10 and around a takeup roll or stretch roll 11 and a skewed idler roll 12 (several wraps to insure nonslippage) and then collected on a bobbin 13. The rolls 7 and 8, which are simply one-piece rotating cylinders, that is, idlers, not driven, are preferably grooved so as to prevent the fibers from becoming tangled.

As previously mentioned, it has been found that the stretching must take place on at least two passes of the fiber through the furnace 5, and the stretch on any one pass must be below about 1.5: 1. 1n the apparatus shown in the drawing, the major portion, if not all, of the stretching occurs on the first and last passes of the fiber through the furnace. This is because the grooved idlers 7 and 8 are each one-piece solid cylinders and each of the grooves have essentially the same diameter. However even though little if any stretching occurs on the intermediate passes, it has been found desirable to employ several intermediate passes through the furnace before the last stretch pass in order to insure the removal of essentially all of the foamable materials prior to the final stretch pass which occurs between the grooved idler roll 8 and takeup roll 11. Preferably, 5 or more passes are made and more preferably 9 passes when using an apparatus such as shown in the drawing. Additional passes maybe used if so desired.

The draw ratio employed in the hot draw zone is from above about 1.5: 1 up to the ratio at which the fiber breaks. Typically, draw ratios of from above about 1.5:! to 35:1 are used, and preferably from about 2.0: l to 3.2: l.

The term draw ratio" as is well known is a measure of the degree of stretching during the orientation of a fiber or filament, expressed as the ratio of the cross-sectional area of the undrawn material to that of the drawn material. While any of the several known ways for measuring or determining draw ratio may be employed typically and conveniently in the case of the apparatus of the drawing, the draw ratio is the ratio of the surface speed of the takeup roll 11 to the surface speed of feed or supply roll 3 (assuming of course that the idlers contain grooves of the same diameter).

As previously mentioned, the draw ratio on any one pass must be less than about 1.5:1 to prevent foaming. In the apparatus shown in the drawing, the draw ratio of the first pass may be obtained, for example, by determining the ratio of the surface speed of the idler roll 7 to the surface speed of the supply roll 3, the draw ratio for the intermediate passes by determining the ratio of the surface speed of the idlers 7 and 8, which are essentially the same thereby making the draw ratio zero, and the draw ratio of the final pass determining the ration of the surface speed of the takeup roll 11 to the surface speed of the idler 8.

if desired, the grooved idler rolls 7 and 8 may have varying diameter grooves in order to alter the draw that occurs during any one pass, particularly the intermediate passes, provided the draw on any one pass is maintained below about 1.5:1. For example, by simply varying the diameter of the grooves any desired sequence of stretching and relaxing is possible.

The minimum hot drawing residence time, i.e., the time during which the fiber is being heated, is dependent to a large extent upon the denier of the fiber, or in the case of multifilament bundles such as yarns the number of filaments and their denier. To a limited extent the drawing temperature will also have an effect as higher draw temperatures will enable the draw to be achieved in slightly shorter residence times. Simple experimentation will enable the optimum residence times to be obtained. Typically, however, when fibers having a denier of from about 1 to 20, and yarns of from about 10 to 1000 filaments are used residence times of from about 1 to 50 seconds, preferably 5 to 30 and more preferably 10 to 20 seconds are employed; the shorter residence times being associated with the smaller fiber denier and smaller yarn bundles. 1t is to be understood, however, that higher denier fibers and larger yarn bundles, i.e., more filaments, may be used if so desired, as the invention is equally applicable to monofilaments, and multifilament yarns and threads and the like.

The drawing speed, that is, the speed of the feed roll or supply roll which in the drawing is the roll 3 is above about 20 meters per minute up to the maximum speed attainable with the particular apparatus. For example, with the apparatus of the drawing, drawing speeds of up to about 60 meters per minute can be employed.

In two copending applications entitled Hot Drawing With Independent Freewheeling Idler Rolls" and assigned to the assignee of this invention there is disclosed another suitable radiantly heated drawing apparatus wherein each of the grooves of the idler rolls 7 and 8 are independent, that is, separate grooved rolls each being free to rotate independently of the other, the grooved rolls having only a common shaft or axle. With this type of apparatus, drawing speeds of up to about 200 meters per minute or higher can be achieved. In addition, because each of the rolls are free to rotate independently of the other a greater amount of the drawing may occur during the intermediate passes through the furnace.

The hot drawing is suitably conducted at a temperature of above about 350 C. up to about the degradation temperature of the polybenzimidazole fiber, preferably from about 450 to 650 C., and more preferably from about 500 to 550 C.

The apparatus of the drawing may be modified, for exam- In each of the above runs I to 3 no foaming occurred. However, when the same foamable polybenzimidazole yarn is subjected to a draw treatment under the same conditions. for example, using a hotshoe, plate or pin, foaming will occur or if pie, by enlarging the area within the furnace 5 such that the 5 all of the draw is attempted on one pass through the radiantly grooved tions 7 aSiGS lmzz yubeS pllacegl wihirzwthstzsgumacfi or heflisd furna e ftoamingwilloccur. r bl t h oven as s own in o at. o. ,8 issue on e inven ion is Y a so app ica e o i 0 er Oct. 1, 1957 to H. H. Schenker entitled MultiStep Stretching p y imi z les uch as those specifically mentioned of Nylon Cords." However, even with such an arrangement esf re Whether in monoor multifilament form. sentially all of the heat supplied to the fiber or yarn is radiant l0 p g p P f f z ei gj 3 PDT:- heat, ve little if an heat bein su lied to the fiber because 0 e l- Invention ave a c ,of conta zt with the gi ooved roll: wifliin th f wh h foregoing specification. However, it should be understood that grooved rolls are within the furna e h pass between h the invention which is intended to be protected herein may be is considered a pass through the furnace for the purposes of 5 Pgactlced qz fi g d l f b depanmg from this invention. l t escopeo t eappen e caims. Any other apparatus suitable for radiantly heating the fibers A p ocess f r h t a ng f ama le p lybenzimidazole such that the fibers can be passed therethrough at le t twi e strand material, which comprises hot drawing the material at a and drawn on at least two passes may be u ed, draw ratio of above about 1.5:] to 35:1 at a drawing speed in The resulting hot drawn polybenzimidazole fibers or yarns excess of about meters per minute in a drawing zone (strand materials) of the present invention are characterized 20 h r in essentially all of the heat supplied to the strand by a high degree of thermal stability and show great resistan e material 15 radiant heat; wherein the draw lS effected on at to degradation by heat, hydrolytic media and oxidizing media. least P 0f l h m zl l f ggii d g :1 am: n s'nau.:;anwere eraw They ma): be used example In apphcanons Such-as space xiii iiiifr g is f ro m a bou t 350C u to about the de radation suits, parachutes, high-temperature dust collector bags, non- P P 8 flammable clothing and fabrics, and the like. temperature of the polybenzimidazole strand material. I

The invention is additionally illustrated in connection with f-be f: :mCl S Oils] Clamt ll where":] an aromatic the following example. p0 y nzimi azo e stran materia is emp oye 3. The process of claim 1 wherein the polybenzimidazole is EXAMPLE poly-2,2-( m-phenylene)-5,5'-bibenzimidazole. A foamable polybenzimidazole y namely p y 4. The process of claims I wherein the strand material is a hen I 5 I h b r r d polybenzimidazole fiber. 5 y 22:32: th g i g i 5. The process of claims I wherein the strand material is a y z t f a I e m f 2 1 polybenzimidazole yarn having from 10 to i000 filaments T e E 0 f use m eac e z each filament having a denier of from about l to 20.

e eac yam waspasse secon s 6. The process of claim 1 wherein the draw temperature is total residence time in furnace) through a radiantly heated 5 o d t t th t h th d in the range offrom about 450 to 650 C. rg zone or appara Us Sum ar 0 a 5 Own m e 7. The process of claim 6 wherein an aromatic polybenzimidazole strand material is employed. f J f or f that to hot drawing had the 8. The process of claim 6, wherein the draw ratio is from Pmpemes' 40 about 2.0;1 to 3.21.

9. The process of claim 8 wherein the strand material is a 3x32222222: if) plybenzimidazle fiber Tcna city (grams pcrdcnicr) 1.7 10. The process of claim 8 wherein the strand material is a TE in 18.2 polybenzimidazole yarn having from 10 to 1000 filaments,

each filament having a denier of from about 1 to 20.

11. The process of claim 8 wherein the polybenzimidazole is The draw temperature in each of the runs was 520 C. poly-2,2-( m-phenylene)-5,5'-bibenzimidazole.

TABLE I Meter/minute Denier Tenacity, Feed Take-up Draw per Elongation, grams/ Run r roll ratio filament percent denier TE 1/2 ""IE1/2Index of fiber organization wherein T is tenacity at break in grams per denier and E is elongation in percent extension from original length at break in tensile test' Ail explanation of this test and its significance is given in the Textile Research Journal 36,

N0. 7, pp. 593-602, July 1966.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 522 :65!) Dated November 23 1971 lnvent fl Georqe F. Ecker Q Thomas C. Bohrer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, lines 16-17, delete "however, that when foamable polybenzimidazole fiber, as hereinafter defined,"

Column 1, line 25, delete "pi" Column 1, line 40, delete "on" Column 2, line 4, delete "us" and insert -is Column 2, line 5, insert -above-- after "of" Column 3, line 10, delete "form" and insert -from Column line delete "p ybenzimidazolene" and inse t Ybenzimidazole- Column 3, line 39, insert before "m" Column e 48, delete "polybenzimidazolene" and insert --P0lybenzimidazole-- Column 3, line 53, delete "are" and insert and Column 3, line 70, delete "powered" and insert -powdered- Column 3, line 74, delete "ad" and insert -as Column 5, line 1, insert not-- after "is" Signed and sealed this 11th day of July 1912:.

(SEAL) Attest:

EDWARD MJLEICI-IER, JR. ROBERT GOTTSCIIALK Attesting Officer Commissioner of Patents :ORM PC4050 USCOMM-DC 60376-P69 U.S GOVERNMENT PRINTING OFFICE: l9! 0-3..13' 

2. The process of claim 1 wherein an aromatic polybenzimidazole strand material is employed.
 3. The process of claim 1 wherein the polybenzimidazole is poly-2,2'' -(m-phenylene)-5,5'' -bibenzimidazole.
 4. The process of claims 1 wherein the strand material is a polybenzimidazole fiber.
 5. The process of claims 1 wherein the strand material is a polybenzimidazole yarn having from 10 to 1000 filaments each filament having a denier of from about 1 to
 20. 6. The process of claim 1 wherein the draw temperature is in the range of from about 450* to 650* C.
 7. The process of claim 6 wherein an aromatic polybenzimidazole strand material is employed.
 8. The process of claim 6, wherein the draw ratio is from about 2.0:1 to 3.2:1.
 9. The process of claim 8 wherein the strand material is a polybenzimidazole fiber.
 10. The process of claim 8 wherein the strand material is a polybenzimidazole yarn having from 10 to 1000 filaments, each filament having a denier of from about 1 to
 20. 11. The process of claim 8 wherein the polybenzimidazole is poly-2,2'' -(m-phenylene)-5,5'' -bibenzimidazole. 